This application relates to a dual action check valve associated with a selectively driven fan having a bypass flow.
In modern aircraft, air for use in the cabin, the cockpit and for other uses on the aircraft typically requires conditioning. In one known system, an air cycle machine provides air to locations on the aircraft. The air comes from a source of relatively hot air and is desirably cooled. The air being delivered into the aircraft passes through a heat exchanger pack, and ram air from outside of the aircraft is brought across the heat exchangers to cool the air to be used on the aircraft.
Typically, a ram air fan is provided in the heat exchanger pack and draws air across the heat exchangers when the aircraft is on the ground. When the aircraft is in flight, the movement of the aircraft may provide a power source for moving the air across the heat exchanger pack.
In the air, or at altitude, the fan capacity is limited. Thus, a check valve typically opens that allows the ram air to bypass the fan.
The fan is positioned downstream of the heat exchangers in the heat exchanger pack. On some occasions, the flow passages for the ram air through the heat exchangers may become clogged due to the impurities in the air. When this occurs, the flow of air to the fan may be less than desirable. The insufficient air can cause a condition called “surge” which can be detrimental to the fan.